This invention relates to an ocean-going ship which is constructed so that it has no one side or on both at least one side port for loading and unloading, and to a system for loading and unloading this ship. The ship according to this invention is particularly suitable for transporting forest industry products, but it can also be used for transporting other mixed cargoes and bulk materials.
A typical transport chain for transporting mixed cargo consists of the following phases:
Storage at mill PA1 Transport to harbour terminal PA1 Storage and handling in harbour terminal PA1 Loading the ship PA1 Ocean transport PA1 Unloading the ship PA1 Storage and handling in the receiving terminal PA1 Transport to customer
The chain involves numerous handling stages. To keep total costs down, handling costs should be low and damage to the cargo minimized. One way to achieve this is to handle and transport the cargo in as big units as possible. In this way, the number of handling times is reduced and efficiency is improved. This is particularly important in the the harbour and during ocean transport, because a ship's transport capacity is decisively dependent on the time it spends in harbour, and the damage to the cargo is dependent on the number of handling times.
It follows from mathematical laws that the bigger the cargo space, the greater the filling degree achieved when loading it for example with miscellaneous forest industry products, such as pulp, paper rolls, sheeted fine paper, sawn timber. The unused space between cargo items is minimized.
The forest product industry's transport requirements often include imports of chemicals, salt, china clay, coal and wood chips. It is advantageous for the industry if the same degree of transport efficiency can be achieved with these bulk products, using the same transport equipment. This allows economical return cargo transport.
Because the strive towards greater efficiency particularly in harbours often leads to irregular working hours, it would be a major advantage if the desired efficiency were achieved inside a normal 8-hour working day.
There are several transport systems on the market for handling the above-mentioned transport requirements. They can be roughly divided into the following main groups:
1. The RoRo system (roll on/roll off), in which the cargo is moved on wheeled trailers into the ship, with the trailers following the cargo to the receiving harbour. The trailers can be used between the harbour terminals or in some cases for taking the cargo all the way to the customer. This system is particularly common for transporting paper. Its main advantage is the small number of handling times. Its main disadvantage is the large amount of stowing and lashing work in the loading terminal and the ship, which has to be done manually. The efficiency in loading and unloading the ship is satisfactory. Because of the large amount of work in the terminal and expensive special ship structures, this system is expensive. The use of space in the ship's cargo hold is very inefficient. This leads to large vessel size in relation to the cargo voume. In addition, the many tween decks in the ship have to be reinforced to withstand the handling and transport of heavy loads on small wheels. The systems is not suitable for transporting bulk cargoes and also requires specially designed harbour-based equipment (for example interface with vessels' ramps and other special structures) especially in tidal harbours. The standard units weigh 30 tons.
2. The Sto-Ro (Stowable RoRo). In this system the load is transported by trailer into the ship where the cargo is stowed using lift-trucks. The trailers do not follow the cargo. The loading efficiency in this system depends on the handling capacity of the lift-trucks. The top limit is determined by the maximum number of lift-trucks that can work with one trailer or in one stowing area. The main disadvantages of the system are the strick requirements for a homogeneous cargo, and the limited possibilities of improving loading and unloading efficiency. Bulk cargoes cannot be transported with this system. For technical reasons, the ship is expensive, with load units normally in the range of 1 to 4 tons. When using flats or containers the maximum unit size is up to 30 tons.
3. The side port system. In this system an elevator arrangement takes the cargo through a port in the side of the ship to the various decks. The cargo is handled by lift-trucks. The trailers do not follow the cargo into the ship. The system puts fairly small requirements for harbour facilities. The system is not suitable for transporting bulk cargoes. The system's loading and unloading capacity is limited (for the same reasons as in item 2 above). The units handled normally weigh from 1 to 4 tons.
4. The LoLo (lift on/lift off) system. The LoLo system is the oldest of all systems described here. In this system, the cargo is hoisted into its final place in the ship's hold by cranes. On-board cranes are either gantry cranes or revolving deck cranes. Gantry cranes have been used to hoist 30 to 40-ton loads (for example containers or wood pulp), but the possibilities of developing the system are limited by its poor suitability for handling mixed products such as paper rolls, paper pallets, sawn timber etc. in the same cargo. Following the growing degree of processing in the forest products industry, there is a clear trend towards mixed cargoes. In the LoLo method several cranes are typically used simultaneously. This leads to difficulties with unexpected heeling of the ship as unit sizes increase. Because of the heavy weight of the crane itself, bigger cranes sizes are not possible, except on the very largest ships. Low overhead cranes cannot be used because of the space needed for deck cargo. The LoLo system can be used for handling bulk cargoes, but it requires complicated and expensive shore-based loading and unloading systems.
Combinations of the above-mentioned systems are also used to some extent.
The object of the invention at hand is to get a ship which allows better economy in ocean transport of mixed cargoes by increasing the ship's annual transport capacity, which is achieved through a signiticant reduction in the time that the ship spends in harbour. Another object is to get a ship that allows transport of mixed cargoes and bulk cargoes in the same ship (return cargoes). A further object is to get a ship which makes use of existing harbour facilities for loading and unloading without any special shore-based structures.
The increase in transport capacity for mixed cargoes is based on the use of large transport units. In other words, one object of the invention is to create a cargo unit of more than 100 tons, compared with conventional unit sizes of 20 to 30 tons. A further object is to create a cargo unit that is constructed so that it allows bulk cargo to be transported in the same ship, while at the same time carrying the full number of empty cargo flats.